00' Mercruiser 5.7 EFI stalling out when up to temp

Well, I won't make this a long story but seems kinda strange to me. Once the engine is up to temp (about 165-170) it sputters and stalls out. Took it for a cruise first thing this year up the severn river and was find just running about 2K RPMs. Then winded it out and was great, but slowed down to close to idle and sputtered. Got it to restart lucky and got back to the marina to have it stall when I was pulling in the slip. So I was told could be water in tank(only left it half full all winter but put stabilizer in it) But had new Fuel filters and seperator put on a week before. Then thought could be a bad impeller? But had that replaced at the beginning of the 05 season. Could it be a thermostat issue? Just not sure what direction to troubleshoot? Thanks for any advice!

Re: 00' Mercruiser 5.7 EFI stalling out when up to temp

Bad impellers and thermostats cause cooling problems, not stalling.<br />If it stalls, you are loosing something needed to keep it running. Fuel is the most likely. Change the fuel filter and check for water. When was the last time the engine was tuned up (plugs, cap, rotor etc.)

Re: 00' Mercruiser 5.7 EFI stalling out when up to temp

Thanks, will check the cap and rotor, had the mech check the plugs and he "said" they are good but we'll see. I'm pretty sure they were replaced as well as the cap\rotor at the beginning of last year, but I will have to double-check my records. Also I mentioned the fuel filter was just replaced but either way could be water in the gas or just needs some fresh stuff.